Electron discharge device circuits



March 30, 1943.

W. J. BROWN i l ELECTRON DISCHARGE DEVICE CIRCUITS 9 Pure or usrsrac:

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MAAAAMALAAA "u" AAAAAAA LOW FREQUENCY Y EQUAL IZER HIGH FREQUENCY AAAAAAAAAA Alun. 'UHU' l IL I I 54- EQUAL/zeneA LAST GRID 0F I3 r/Rsr su? l PLA s or 57 PLA ak/o oF F/Rsr STAGE PLATE of 457512165 /NVENTOR i v W J. BROWN ATTORNEY Patented Mar. 30, 1.943 l ELECTRON DISCHARGE DEVICE CIRCUITS William J. Brown, Hackensack, N. J., assignor to Western Electric Company, Incorporated, a corporation of New York Application January 21, 1939, Serial No. 252,113

l2s claims. (cl. 179-171) 'I'his invention relates to electron discharge device circuits, and, more particularly, to electric wave amplifying circuits or systems using electron discharge devices and to a method and means for regulating or controlling the volume or level of the output of such amplifying circuits or systems.

A conventional method of and arrangement for A obtaining amplifier volume control is to utilize a negative feedback by taking or deriving a pora more complete understanding of the invention will be which follows, taken in conjunction with the appended drawing, wherein:

Figs. 1 and 3 are simplified showings of a circuit embodying the invention;

tion 4of the output voltage of the amplifier and feeding it back through a sliding or adjustable contact. to a cathode resistor in a preliminary stage. A difficulty in doing this is that variation in the sliders position on the cathode resistor produces considerable noise if the ampliiler has even a moderate amount of gain.

An object of the invention is to regulate or control the output volume of an amplifying circuit or system utilizing negative feedback, and yetueliminate or minimize the introduction of noise as a result of adjustments of the control means.

Amplifiers have been operated in parallel heretofore, but the most satisfactory results have been obtainable only when the amplifiers have been matched closely in al1 their characteristics.

Another object of the invention, therefore, is to operate in parallel amplifiers of dissimilar gain and response characteristics, and yet obtain substantially the same effects as if the amplifiers had exactly similar characteristics.

It is frequently desirable to be able to use an amplifier of push-pull type, but the input available may be unbalanced. If means are-interposed between the source of unbalanced input and the amplifier for deriving a balanced input to the push-pull amplifier, this difficulty is obVIated. In order to obtain the advantages of a stabilized negative feedback ampliiier,'it may be desired to provide a negative feedback con- A nection, but the manner in which this is to-be done is not an obvious one.

Still another object of this invention, therefore, is to enable a source of unbalanced input signal to be coupled to a balanced or push-pull Fig. 2 shows the circuit arrangement'of a twostage amplifier with an intermediate inverter stage coupling a single tube amplifier with a push-pull amplifier, embodying the invention;

Fig. 4 shows a circuit arrangement of two ampliiiersconnected for operation in parallel andv having a common feedback connection in accordance with this invention; and

Fig. 5 shows a modification of the feedback resistance and cathode resistors circuit of the amplifier, and to provide4 negative feedback of energy around the amplifier.

The manner in which these and other objects of the invention are realized will be evident, and

circuit arrangement of Fig. 4.'

The circuit arrangement of Fig. 1 comprises input terminals electron discharge device circuit or system I2, more lspecically, an amplifying circuit or system embodying a negative feedback connection of the type disclosed and claimed in H. S. Black Patent 2,102,671, issued December 21, 1937, i. e., one in which a portion of the output energy is fed back to a preliminary part of the circuit in such phase and of such magnitude'that the overall gain of the amplifier is reduced substantially below what it vwould have been if there were no feedback of any kind present; an output transformer I3; and output terminals I4'. The amplifier I2'is shown as general in character and as one whose output volume is regulatable or conl trollable by variation in the amount of energy fed back to a preliminary part of the amplifier from a part nearer the output. It is assumed, however, for the purpose of this disclosure, that the amplifier I2 is a multistage ampliiier having an even numberof stages, and that the cathode of the initial stage is provided with a cathode resistor I5. The feedback connection I6, in accordance with this invention, is from. the plate of the last stage of the amplifier through a blocking condenser I 'l and resistance I8 to the low potential end-of the cathode resistor, a condenser I9 being connected between the feedback resistance I8 and the cathode resistor, one side ofv the condenser being connected to theA endv of cathode resistor nearest the cathode and the other side of the condenser being connected to obtained, from the detailed description I0; an input transformer II; an

a slide' or contact 20 adapted for adjustable engagement with and along the length of resistance I8.

I'he arrangement heretofore used to obtain output volume control by variation of the amount of negative 'feedback in a stabilized negative feedback amplifier has been one in which the condenser I9 and resistance I8 were not used, the feedback connection I6 being' made through a slide orcontact directly to the cathode resistor I5. As pointed out hereinbefore, that arrangement has been found to introduce considerable noise in' the output when the slide or contact is altered. There is a potential drop acrossv the cathode resistor; as the slide is moved along it, there will be sudden or abrupt changes in potential from one slider position to the next, i. e., between taps; or between turns, if the resistor is of the wire-Wound type; or,.if the resistor is of the composition type, due to the shunting out of a small section as the slide is moved along it. These changes are amplified by the amplifier and appear as noise inthe output. By use of the additional resistor or resistance I8 and the condenser I9, extremely quiet operation of the volume control is obtained.

In addition to having the advantage of lquiet operation, the amount of feedback around the output tube of a multistage amplifier is not reduced as much as the gain of the amplifier is increased. This occurs because the condenser. I9 acts as a by-pass condenser around the cathode resistor. In an amplifier to be described more particularly with reference to Fig. 2, it was found that, over the major portion of the volume control range, the feedback voltage around the final stage is altered approximately one-half the 'amount-of the change in gain. By appropriate selection of resistance and capacitance values for Y resistors I5 and I8 and condenser I9, it is possible to obtain considerable variation' in the relationship between the amount of feedback and the change in gain.

In Fig. 3, the subject-matter of Fig. 1 `is presented in somewhat; different aspect. The feedback connection maybe represented as a shunt across the secondary of the output transformer I3. The blocking condenser I1 is not required since the connection is no longer on, the primary. side of the transformer. The cathode resistor I5 systems. The ampliiierZI comprises an initial amplifying stage 22 coupled through a phase inverter stage 23 to a push-pullamplifler'stage 24 theoutput of the latter being coupled through the output transformer 25 with the output terminals 26. Amplifying vstage 22 comprises'. a pentode 21 whose cathode 28 is provided with a cathode resistor 29. This amplifying stage is resistance-capacity coupled to' the inverter and the push-pull stages. The inverter stage comprises a pentodev30 whose screen and Asuppressor grids 3|, 32 are tied to the plate 33, and whose cathode 34 `4is' provided with anv unbypassed rethe screen grids and the plates of the tubes may be supplied from an alternating current source 39,' through transformer 40, full wave rectifier 4I, potentiometer t2, and associated by-pass condensers 43-46. Control grid bias for the tubes 31, 38 is provided bybiasing resistor 41, shunted by signal frequency by-pass condenser 48.

The connection 49 is a negative feedback connection similar to that of Fig. 3, the feedback resistor or resistance 50, the condenser 5I, the cathode resistor 29 and slide 0r contact 52, corresponding to the parts designated by numerals I8, I9, I5 and 20 in Fig. '3, but includes a low and a high frequency equalizer 53, 54, which were employed in an amplifier constructed in accordance. with Fig. 2, so that the energy feedback was equally effective over the entire frequency range.

Not only-does the amplifier 2I embody the volume control feature of this invention, it also embodies the feature of an amplifier having an over-al1 stabilized negative feedback connection, and a local degenerative or -negative feedback in an inverter stage coupling a single amplifying tube to a push-pull amplifier stage.

The circuit arrangement described with reference to Fig. 2 enables application of an unbalanced input .to the inputstage of the amplifier and the deriving of push-pull or balanced output therefrom by use of a phase inverting stage and the amplification of\such balanced output in a Apush-pull amplifying stage, with an over-all negative feedback connection from the output of -the amplifier to the input circuit of the stage of which the unbalanced input is applied.

Fig. 4 is a circuit arrangement yembodying this |invention as applied to the operation in parallel of two stabilized negative .feedback amplifiers of different characteristics. The amplifiers 456, 51

may vbe the same type as amplifier 2I but of different gain and/or response characteristics, and modified as pointed out hereinafter. The common input terminals 58 are coupled through the transformers 59, 60 to the input terminalsv 55 of the ampliiiers and the common output terconnection is made from the slide or contact 66 through the condensers 61, 68 with the ends of the cathode resistors 29 near the cathode. As

sistor 35 for biasing the control grid J6 and for 75 shown in Fig. 5, a single condenser 69 could be substituted for the two condensers 61,68, one terminal of such condenser 69 being connected to the slide 66 and the other to the high potential ends of the resistors 29. e

Experiments conducted upon two similarl amplifiers resulted in a'n exact doubling oftheir load capabilities when`paralle1 through a common feedback path. Deliberately making the A gain and the response characteristics of one differ from that o! the other made substantially no :,siaafa difference, the results being comparable to those obtained when the amplifiers had exactly similar characteristics. y

The factthat this invention has beenwdisclosed with reference, to various speciiicembodiments is not intended as a` limitation of the invention thereto, .the scope offthefnvention being evidenced by the appendedjclaims;

What is claimed ist:v 'y

l. An audio frequency amplifier'comprising an initial amplifying stage, a second, amplifying stage, means coupling said stages together, said initial stage comprising. an electron,discharge device havingacatho'de, an anode and a control grid, aresistor common to thegrid-cathode and l cathode-anode circuits of said device, and means for adjusting the over-all gain of said coupled stages'comprising a gain reducing feedback connection from the output ofV said second stage tov i th'efle'nd of said resistor remote from said cathode,

said connection including means to equalize the feedback in the frequency rangeto be amplified `and a, second resistor, the two resistors being connected together througha condenser :one terminal of which is connected tothe cathode end of said first resistor and the other terminal of vwhich is connected tv o meansmaking an adjust- `able .contact with saidsecond resistor, adjust-V ments of saidlatter means varying theamount of .negative feedback and the over-all gain of the combination with substantially no noise being added to `,the amplified output.

2'. In a sound reproducing.system,`the combination `witha pluralityof amplifiers having their inputs and youtputs vconnected together, of a single negativen*feed-backcircuit feeding back a portion of ther combined',outputs tothe inputs of bothamplifiers,...V l ,n

3, The c" mbinationwith' aa'plurality of power amplifiers` lhaving their inputs and combined end outputs arranged in parallel,v of asingle negative feed-back circuit feeding back a portion of the 1combined outputs to the inputsof both ampliers. M

'4. The combination with afplurality of amplifiers having vtheir inputsand their .outputs connectedtogether;I of a` common'feed-back circuit feeding baci: `a portion-ofr the combined outputs -to the inputs of both amplifiers.

5. In a sound reproducing system,.the combination with a plurality of amplifiers having their inputs and outputs connected together, of a single negative feed-.back circuitconnecting. the combined outputs of the amplifiers-back to their inputs and an attenuation equalizer arranged in the feed-back circuit.. v 5

6. .The combination with a plurality of amplifiers had exactly similar characteristics, said means comprising a single circuit connection common to said amplifiers for feeding back a part of their combined output to their input circuits.

9. In combination, two amplifiers of dissimilar characteristics having common input and common output circuits, and means for equalizing said amplifiers so that their combined output is substantially what it would be if the. ampliers had exactly similar characteristics, said means comprising a single circuit connectioncommon to said amplifiers for feeding back a part of their combined outputs to their input circuits, the initial stage of each amplifier comprising a cathode resistor, and said feedback connection including a resistance having a portion thereof in series and another portion in parallel with each cathode resistor.

10. In combination, two amplifiers of dissimilar characteristics having common input and comode resistor, and said feedback connection infiers having their inputs and outputs arranged yin parallel, of a single negative feed-back circuit feeding back a portion of the combined out- `puts to the inputs of both ampliflersand means,

arranged in the feed-back circuit, for controlling the frequency response characteristic of the amplifiers.

7. The combination witha plurality of amp1i.1 vfiers having theirinputs and their outputs connected together, of a single feed-back circuit common to said amplifiers and means, arranged in the feed-back circuit for determining the frequency response characteristic of the ampliers.

cluding a resistance having a portion in series and another portion in parallel with each cathode resistor, capacitance means being connected between said feedback resistance and the cathode resistors.

l1. In the amplification of an electric wave by la plurality of multistage amplifierseach having an input circuit and an output circuit, the amplifiers being of dissimilar frequency response characterist'ics, the input circuitsbeing connected in parallel and the output circuits being connectedA in parallel, the method of equalizing for the effect of the separate amplier characteristics on the combined output from the amplifiers of the electric wave being amplified, that comprises applying to each input circuit in phase opposition to the electric wave applied thereto a portion of the combined amplified output of the amplifiers.

12. In the amplification of an electric wave by a plurality of multistage amplifiers of dissimilar frequency response characteristics, each having an input circuit and an output circuit, the-method that comprises applying the electric wave to the input circuits simultaneously, combining the ampliied Wave outputs appearing in the output circuit of each amplifier, deriving the amplified electric wave from' said combined output, and applyving a portion of said derived wave to the input circuit of each amplifier in phase opposition to the electric wave to be amplified.

13. In the amplification of an electric wave by a plurality of multistage amplifiers of dissimilar frequency response characteristics, .each having an input circuitand an output circuit, the method that comprises applying the electric wave to the input circuits simultaneously, combining the amplifled v'ave output appearing in the output circuit of each amplifier, deriving the amplified elec- 8. In combination,.two multistage amplifiers of l dissimilar characteristics having common inputandcommon output circuits, and means for equalizing said amplifiers so'that their combined out'- put is substantially what it would be if the ampli- 'tric wave from said combined output, and applying a portion of said derived wave to the input circuit of each amplifier in phase opposition to vthe electric wave to lbe amplied and in magnitude such as to reduce substantially/the over-al1 gain of said amplifiers compared to the over-all gain thereof if no derived Wave were applied to the input circuits o'f the amplifiers.

the amplifiers.

amplifiers of dissimilar gain and frequency response characteristics, each amplifier having an input circuit and an output circuit, the method that comprises applying the audio frequency wave tothe input circuits simultaneously, combining the amplified wave output appearing in the output circuit of each amplier, deriving the amplified electric ,wave from said combined output, and applying a portion of said derived wave to the input circuit of each amplifier in phase opposition to the electric wave to be amplified and in magnitude sufficient to reduce substantially the over-all combined gain of said amplifiers compared to their combined gain if no derived wave were applied to the input circuits of 15. The combination with a plurality of audio frequency-amplifiers having their input circuits connected together and their output circuits connected together, of a feedback circuit common to said amplifiers feeding back a portion of the combined output of said amplifiers to the input circuits of said amplifiers.

i8. The combination with a plurality of audio frequency amplifiers having their input circuits l connected together and their output circuits connected together, of a feedback circuit common to said amplifiers feeding back a portion of the combined output of said amplifiers to the input circuits of said amplifiers to reduce the overall combined gain of said amplifiers.

17. The combination with a plurality of audio frequency ampliers having theirvinput circuits i connected togetherand their output circuits connected together, of a feedback circuit lcommon to said amplifiers feeding back a portion of the combined output of said amplifiers to the input l circuits of said amplifiers in phase opposition cluding means to control the frequency response characteristic of said combined ampliers.

19. The combination with a plurality of audio nected together, of a feedback; circuit common to said amplifiers feeding baci; a portion of the combined output of said. amplifiers tothe input circuits of said amplifiers, said feedback circuit including an attenuation equalizer. Y

20. In combination', two multistage ,audio frequency ampliers of dissimilar characteristics having common input and common 'piitput circuits, and'means forequalizingl saidi'ampliers so that their combined output. is substantially what it would be if the amplifiers had exactly similar characteristics, said means lcomprising a single circuit connection common to said amplifiers for feeding back apart of their combined output to their input circuits.

21. In combination, two multistage audio fre-- quency amplifiers of dissimilar characteristics having common input and common output circuits, and means for equalizing said amplifiers so that their combined output is substantially what it would be if the ampliiersfhad exactly similar characteristics, said4 means comprising a single circuit connection common to said amplifiers for feeding back a part of their combined output to their input circuits in phase` opposition to v.the audio frequency electric wave applied to said input circuits to be amplified.

22. In combination, two multistage audio frequency amplifiers Iof dissimilar characteristics having common input and common output circuits, and means for equalizing said amplifiers so that their combined output is substantially what it would be if the amplifiers had exactly similar characteristics, said means comprising va single circuit connection common to said amplifiers for feeding back a part of their combined output to their input circuits to reduce substantially the combined gain of said ampliers compared to what the combined gain would fbe if no feedback connection were provided.-

23. In combination, two amplifiers of dissimilar characteristics having common input and common output circuits, and means for equalizing frequency amplifiers having their input circuits said amplifiers so that their combined output is substantially what it would be if the amplifiers had exactly similar characteristics, said means .comprising a single circuit connection common to said amplifiers for feeding back a part of their combined output to their input circuits to reduce the combined gain of said amplifiers below what the combined gain would be if no feedback connection were provided.

. WILLIAM J. BROWN. 

